A wide variety of heart valve prostheses have been developed to operate hemodynamically, in conjunction with the pumping action of the heart, to take the place of defective natural valves. These valves variously have valve bodies which are designed to function either with a single occluder or a pair of occluders or leaflets, which occluders generally pivot along eccentric axes (or both pivot and translate) to open and close a central blood flow passageway through the valve body.
U.S. Pat. No. 3,546,711 (Dec. 15, 1970) shows a single occluder valve wherein a circular disc pivots about a fixed axis which is offset, in the downstream direction, from the plane of the occluder in the open position.
U.S. Pat. No. 4,373,216 (Feb. 15, 1983) discloses both single occluder and bi-leaflet heart valves wherein protrusions extend generally radially inward from a pair of flat sidewall sections of the valve body. Valve members, which have slots in their lateral edges to receive such protrusions, are guided in generally pivoting about an axis adjacent the upstream edge thereof and translating to reach their closed position.
U.S. Pat. No. 4,308,624 (Jan. 5, 1982) discloses heart valves of both the single occluder and bi-leaflet type having curved valve members which both rotate and translate in moving between the open and closed positions. Although the leaflets were intended to be able to assume a parallel orientation in the open position, as shown in FIG. 3, study of the valve arrangement shows that, upon reversal of blood flow through the passageway, although pivoting could occur in the intended manner, the leaflets could also translate upstream without beginning to rotate toward the closed position. Once the leaflets have so moved upstream (having been guided by the paths the spherical ears trace in the slots 21), one or both of the leaflets might possibly counterrotate because of the instantaneous attitude of bloodstream flow and, as a result, not close on that stroke. U.S. Pat. Nos. 4,328,592 and 4,443,894 (Apr. 24, 1984) disclose later versions of this valve; both illustrate embodiments wherein the leaflets in their open position are angled relative to the centerline plane (see Column 4, lines 39-43 of the U.S. Pat. No. '894 patent). Thus, when flow reversal occurs (as depicted in FIG. 4), because of the alignment of angled surfaces 44 of the stops 41 and the placement of the stops, potential inward pivoting or counterrotation of the leaflets is precluded (see Column 5, lines 34-41).
U.S. Pat. No. 4,363,142 (Dec. 14, 1982) discloses a bi-leaflet heart valve wherein the leaflets have laterally extending ears in the form of generally oval or spherical projections that are received in recesses of complementary design.
U.S. Pat. No. 4,451,937 (Jun. 5, 1984) shows additional single occluder and bi-leaflet valves wherein valve members pivot and translate to their closed positions, being guided, in part, by laterally extending ears 21 which move in generally arcuate slots or depressions 23. The valve members are of necessity oriented at an angle to the centerline plane in the open position.
U.S. Pat. No. 4,692,165 (Sep. 8, 1987) discloses single occluder and bi-leaflet valves wherein valve members have notches in their lateral edges which receive arcuate posts protruding from flat sidewall sections of the valve body; the posts and associated stops guide the pivotal and translational movement of the valve members.
U.S. Pat. No. 4,863,458 (Sep. 5, 1989) discloses bi-leaflet heart valves having leaflets of varying thickness which are guided in generally pivotal movement by laterally extending ears 54 that are sectors of a sphere and are received in modified, generally spherical recesses 48 formed in the flat sidewall sections of the valve bodies. The ears each have a flat, inboard surface 53 but otherwise have a spherical surface 55 (see FIGS. 5 and 9). The flat surface 55 engages the flat stop surface 97 in the full open position wherein the leaflets are oriented at a substantial angle to the centerline (see FIG. 2) So that the backflow of blood will cause prompt pivoting to the closed position.
U.S. Pat. No. 4,808,180 (Feb. 28, 1989) discloses a bi-leaflet valve wherein the leaflets each have a semi-conical shape and thus inherently provide significant resistance to blood flow through the valve in the open position. The leaflets are guided by generally C-shaped rails (FIG. 3) that protrude from the valve body sidewall and that are received in recesses of complementary shape in the lateral edges of the semi-conical leaflets (FIG. 5).
Commercially developed heart valves, using valve members of the type generally exemplified by various of the above-mentioned U.S. patents, have always employed those valve members oriented at an angle to the centerline plane in the open position so that, when backflow of blood begins, it preferentially impinges upon the outflow surfaces of each valve member and thus initially imparts a pivotal component to its closing movement. It is now felt to be particularly important that a mechanical heart valve prosthesis should provide a passageway through which blood can flow freely in the open position with a minimum of drag. To accomplish this desired objective, it is now believed that the valve members should be able to assume a low-energy orientation which is usually parallel to the longitudinal axis of the passageway; however, in such orientation, the valve members must still be highly responsive to backflow so as to close quickly with a minimum of regurgitation. Improvements in valve construction have continued to be sought with the objective of creating mechanical valves having such characteristics.